Flame responsive safety control system using prism and light chopper



1957 J. r. ATOR 2,804,131

FLAME RESPONSIVE SAFETY CONTROL SYSTEM USING PRISM AND LIGHT CHOPPER Filed June 5, 1,953

sac. 4

IN V EN TOR.

FLAME RESPONSIVE SAFETY CONTROL SYSTEM USING PRISM AND LIGHT CHOPPER Joe T. Ator, San Fernando, Calif., assignor to Generai Controls Co., Glendale, Califi, a corporation of ahfornia Application June 5, 1953, Serial No. 359,863

6 Claims. (Cl. 158-28) The present invention relates to means and techniques for detecting the presence of a flame and for controlling the flow of fuel to such flame.

The problem of detecting the presence of a flame in a furnace gives'rise to certain difliculties, mainiy, because the radiation energy from the heated walls of the furnace may, unless certain precautions are taken, have the same eflect as the radiation energy from the flame itself, with the result that a false indication may be produced, leading to the creation of a dangerous situation.

Briefly, the present invention relates to improved means and techniques for producing an indication or control which takes into account the radiation energy from the heated furnace walls as well as from the flame, and producing what may be termed to be a differential effect which is sufficiently large in magnitude to produce an indication or control, such differential effect being measured in terms of difference in radiation energy between, on the one hand, the radiation energy from the flame, and on the other hand, the radiation energy from the heated furnace wall or any other body which is heated by a flame.

This result is accomplished, generally, as described more fully hereinafter, by directing the combined radiation energy from the flame and walls, on the one hand, and the radiation energy from the walls, on the other hand, alternately onto a single photocell which serves to develop a fluctuating output voltage, such output voltage being amplified by an amplifier which is preferably selective to the frequency of fluctuations that are due to the flame, the output of the amplifier being used to control a solenoid valve which in turn controls the flow of fuel to the flame.

It is, therefore, a general object of the present invention to provide new and improved means and techniques of this character. h

A specific object of the present invention is to provide means and techniques of this character which produce the intended result without substantial interference as a result from either the inherent sporadic fluctuations in intensity of the flame, or induction or pickup of the fundamental or harmonic frequency of neighboring power circuits.

Another specific object of the present invention is to provide an arrangement of this character which is suitable for either gas or oil heated furnaces.

Another specific object of the present invention is to provide means and techniques of this character which obtain the above mentioned differential effect in a novel manner using novel apparatus.

The features of the present invention which are believed to be novel are set forth with particularity in the appended claims. This invention itself, both as to its organization and manner of operation, together with further objects and advantages thereof, maybe best understood by reference to the following description taken in connection with the accompanying drawings in which:

tates Patent fiice Figure 1 illustrates apparatus embodying features of the present invention associated with the flame in a conventional furnace having conventional flame producing means associated therewith.

Figure 2 is a view taken generally on the line 2-2 of Figure 1.

Figure 1 shows a furnace 10 defined by the interior walls 11, 12, 13 and 14. Conventional flame producing means designated by the general reference numeral 16 serves to burn fuel and produce the flame 17. The wall 11 is provided with an opening 11A to allow the novel apparatus now described in detail, to view certain conditions inside the furnace it The optical system, generally, is arranged to receive radiation energy from the flame 17 along the general path designated by the line 20 and to receive radiation energy from the heated furnace wall 14 along the general path indicated by the line 22.

The optical system includes, generally, a prism or radiation energy directing means 30 disposed in the front end of radiation energy tubes 39, 40, a pair of lenses 31, 32, a pair of apertures 33 and 34, a radiation energy applying or collecting cone 36, all of which serves to direct radiation energy onto a photocell 38. The lens 31 is disposed in the first radiation energy channel 39 to focus the radiation energy from the wall 14 onto the photocell 38; and, likewise, the lens 32 is in the second radiation channel 40 to focus the radiation energy from the flame 17 onto the photocell 38. Radiation channels or light tubes 39 and 40 terminate at the apertures 33 and 34, such apertures 33, 34 being alternately and recurrently blocked, in an optical sense, by the rotating apertured disk 59 which is suitably apertured to allow the combined radiation energy from the flame and wall, on the one hand, and the radiation energy from the furnace wall, on the other hand, to impinge on the photocell 38. Such rotation of disk 50 converts the incoming radiation energy into energy pulses. Also such rotating disk 5ft serves as an element for alternately and sequentially applying the radiation energy from channels 39 and 40 onto the photocell 33. As described, the prism 30, of course, directs the radiation energy from the wall 14 into the channel 39 and such prism likewise directs the combined radiation energy from the flame 17 and wall 13 into the channel 40. The apertured disk or shutter 50 is rotated at a relatively high speed by the motor 52 through the flexible belt 53 which passes over, on the one hand, the pulley 55 on the motor shaft and, on the other hand, the pulley 53 on the shutter shaft 59. The shaft 59 is suitably journaled for rotation in conventional bearings (not shown), while the motor 52 is mounted on the floor of the rectangular light-tight box 60 which has the two aforementioned rectangular apertures 33 and 34 therein. The radiation channels 39 and 40 may be either rectangular or circular, but arranged to exclude extraneous radiation from entering the apertured portions 33 and 34.

Thus, when the flame 17 is present the photocell 38 is alternately subjected to the combined radiation energy from the flame 17 and wall, 011 the one hand, and from the wall 14 of the furnace on the other hand. Since the radiation energy from the flame 17 is substantially greater than the radiation energy from the furnace wall 14, the photocell 38 is recurrently subjected to relatively large radiation intensities, with the result that the relatively large and rapidly varying voltage is developed across the load resistance 7%, such load resistance 70 being serially connected with the photocell 38 and source '72. Preferably, the photocell 38 is of the 931A type. The voltage developed across resistance 70 is thus a quantity, the magnitude of which is representative of the'combined radiation energy between, on the one hand, the radiation energy from the flame and walls and the radiation energy from the furnace walls on the other hand, and the cyclical variation of such quantity is in accordance with the speed of rotation of the shutter 50 and the number-of apertured windows 50A in the shutter 50. Preferably this cyclical variation is made relatively high in relationship to the average frequency of the sporadic fluctuations of the flame 17 and sufficiently removed from the fundamental or harmonic frequency of neighboring power supply circuits such as commercial 60 cycle power supply circuits, thereby preventing the determination from being obscured either by the flame flutter or by pickup or induction from neighboring supply circuits.

It is noted that in one revolution of the shutter 50, the photocell 38 sees the flame 17 eight times, i. e., the number of'apertures 50A in disc 5t Further, in one revolution of the disc 50, the photocell 38 sees" the furnace wall twice this amount, namely, 16 times. This is so since the photocell sees the wall 13 when the flame 3-17 is being simultaneously viewed and, in addition, the photocell 13 sees the wall 14 alone when the flame is not being viewed. Consequently, the fluctuating output voltage appearing across resistance 70 may be considered as having two components, namely, a low frequency component corresponding to those fluctuations produced by the flame alone, and a high frequency component, of twice the frequency of said low frequency component.

The cyclically varying voltage having such low and high frequency components thus appearing across resistance 70, when a flame is present, is applied through condenser 76 to the input resistance 77 of the amplifier stage 78. Preferably the amplifier stage 78 is tuned or peaked at a frequency corresponding to the cyclical variation or frequency of such low frequency voltage component developed across resistance 70. Such tuned or peaked amplifier stage 78 thus serves as a means for discriminating between such low and high frequency components of the voltage developed across resistance 78. Tuned amplifiers serving the purpose of amplifier stage 78 are well known in the art and are disclosed in section 7-1 of chapter 7 of Radio Engineering, third edition, by Frederick E. Terman, 1947. The voltage developed at the output terminals of the amplifier stage 78 is applied to the control circuit 80, which is considered conventional for controlling the energization of the solenoid valve 82, such valve 82 serving to control the flow of fuel which normally flows between the fuel inlet line 84 and the fuel outlet line 85 extending to the conventional burner or flame producing means 16. The valve 82 is open when a flame is present, but is allowed to close under the influence of springs conventionally associated with this type of valve, immediately upon cessation of the flame, i. e., immediately upon cessation of the raditaion energy from the flame.

When the flame is extinguished for any reason, there is, of course, no radiation energy from the flame 17 and, as shown in the drawings, the photocell 38 alternately sees the walls 13 and 14 of the furnace and, since these two walls have substantially the same or somewhat different temperatures, the radiation energy from the same is substantially the same or somewhat different. The photocell 38 is, of course, subjected to this difference, but under these conditions a relatively small voltage appears across the resistance 70, and across resistance 77 with the result that the solenoid 82 is allowed to become de-energized, thereby preventing further flow of fuel to the burner.

It is apparent that instead of using a rotary shutter 50 a reciprocating shutter may be used if desired; likewise, the design or shape of the windows 50A, and their number, is considered to be one of design and is preferably such that there is a voltage of relatively large average intensity which varies cyclically and which has a low and a high frequency component as described above, developed across resistance 70 when there is a flame and a voltage of relatively small average intensity which varies cyclically and has only such high frequency component across the resistance when there is no flame. Thus, by the means described above which involves the tuned or peaked amplified stage 78, a differential effect is produced since the channel 39 passes radiation from the fire brick walls 14, while the other channel 40 passes radiation energy emanating not only from the flame 17, but also from the fire brickwall 13, along the path represented by line 20, such line 29 intersecting the inner wall 13. In effect, taking into consideration the frequency selective nature of the amplifier 78, the output of the two radiation channels 39 and 40 is subtracted electrically so that with a flame on condition the net voltage developed across control is considered as that being due to the flame alone and with a flame off condition the net voltage developed across control 80 is considered to be zero.

While a prism 30 is preferred for directing the radiation, other light retracting or light reflecting means may be used, adjusted, however, as described above.

While the particular embodiments of the present invention have been shown and described, it Will be obvious to those skilled in the art that changes and modifications may be made without departing from this invention in its broader aspects and, therefore, the aim in the appended claims is to cover all such changes and modifications as fall within their scope.

I claim:

1. In a flame detecting and controlling arrangement of the character described, flame producing means for producing a flame, a body heated by the flame, means for alternately and sequentially collecting and delivering radiation energy pulses from, on the one hand, said flame and said body heated by said flame, and on the other hand, from said body alone, with the radiation energy pulses from the body, in each instance, being substantially equal and occurring at equally spaced intervals to thereby develop radiation energy pulses varying cyclically at two different frequencies, a radiation responsive electrically operable device operably associated with said collecting and delivering means, means located between said collecting and delivering means and said device for applying said cyclically varying radiation energy pulses onto said radiation responsive device, said device in response to said radiation energy pulses developing a control voltage having two components varying at a low frequency and a high frequency, said low and high frequencies corresponding to said two differing frequencies developed by said cyclic varying radiation energy pulses, and control means responsive to only said "low frequency component of said control voltage to control the flow of fuel to said flame producing means so that the flow of fuel is maintained in the presence of'and discontinued in the absence of said low frequency component of said control voltage.

2. In flame detecting and controlling apparatus of the character described wherein it is desired to control a flame which heats a body, flame producing means for producing a flame, a body heated by the flame, means collecting and delivering radiation energy from, on the one hand, said body and said flame, and, on the other hand, from said body alone, alternately and sequentially, with the radiation energy from the body, in each instance, being substantially equal and occurring at equally spaced intervals, radiation responsive electrical means operably associated with said collecting and delivering means to develop a cyclically varying electical control voltage having low and high frequency components in accordance with said alternate and sequential delivery of radiation energy to said radiation responsive electrical means, and means controlling the flow of fuel to said flame producing means in accordance with only said low frequency component of said control voltage so that the flow of fuel is maintained in the presence of and discontinued in the absence of said low frequency component of said control voltage.

3. In flame detecting and controlling apparatus of the character described, flame producing means for producing a flame, a furnace wall heated by the flame, a first radiation energy collecting and delivering channel, a second radiation energy collecting and delivering channel, means subjecting said first channel to radiation energy from said wall of said furnace, means subjecting said second channel to radiation energy from said wall and also to radiation energy of said flame, a single radiation responsive electrical means operably associated with said first and second channels, means located between, on the one hand said first and second channels, and on the other hand, said radiation responsive electrical means for alternately and sequentially applying the radiation energy from said first and second channels to said radiation responsive electrical means, with radiation energy from the wall, in each instance, being substantially equal and occurring at equally spaced intervals to develop a control voltage which varies at two different frequency components, one at a low frequency in accordance with radiation energy from said flame alone, and the other at a high frequency in accordance with radiation energy from said body alone, frequency discriminating means connected with said radiation responsive electrical means to receive said control voltage with its said two frequency components and to produce an output of only said low frequency component, and control means connected with said discriminating means for controlling the flow of fuel to said flame, said control means being sensitive to said low frequency component so that the flow of fuel is maintained in the presence of and discontinued in the absence of said low voltage frequency component.

4. In flame detecting and controlling apparatus of the character described, wherein a flame heats a body, flame producing means for producing a flame, a body heated by said flame, radiation energy collecting and delivering means, a single radiation responsive electrical means operably associated with said radiation energy collecting and delivering means, said radiation energy collecting and delivering means being located between, on the one hand, said flame and body, and on the other hand, said radiation responsive electrical means, means for alternately and sequentially applying radiation energy from, on the one hand, said flame and said body, and on the other hand, from said body alone, onto said radiation responsive electrical means, with the radiation energy from the body in each instance, being substantially equal and occurring at equally spaced intervals to develop in said radiation responsive electrical means a control voltage having two varying frequency components, one varying at a low frequency and the other at a high frequency, control means for controlling the flow of fuel to said flame, said control means being sensitive and responsive to the presence of said low frequency component, and means receiving from said radiation responsive electrical means said high and low frequency components of said control voltage and transmitting to said control means only said low frequency component so that the flow of fuel to said flame is maintained in the presence of and discontinued in the absence of said low frequency component.

5. In flame detecting and controlling apparatus of the character described wherein a flame heats a body, flame producing means for producing a flame, a body heated by said flame, a single radiation responsive electrically operable device, a first radiation energy collecting and delivering channel, radiation energy directing means cated between, on the one hand, said flame and body, and on the other hand, said device, for directing radiation energy from said body and flame into said first channel, a second radiation energy collecting and delivering channel, said radiation energy directing means directing radiation energy from said body to said second channel, said radiation responsive electrically operable device being operably associated with said first and second channels, means alternately and sequentially communicating said first and second channels with said device, with the radiation energy from the body, in each instance being substantially equal and occurring at equally spaced intervals to develop an electrical control voltage having two components varying at a low frequency and a high frequency, the low frequency corresponding to radiation energy from said flame alone, and the high frequency corresponding to said body alone, control means for controlling the flow of fuel to said flame, said control means being sensitive and responsive to said low frequency, and means receiving from said radiation responsive electrical means said high and low frequency components of said control voltage and transmitting to said control means only said low frequency component so that the flow of fuel to said flame is maintained in the presence of and discontinued in the absence of said low frequency component.

6. In flame detecting and controlling apparatus of the character described wherein a flame heats a body, flame producing means for producing a flame, a body heated by the flame, a radiation responsive electrically operable device, a first radiation energy collecting and delivering channel for delivering radiation energy from said body onto said device, a second radiation energy collecting and delivering channel for delivering radiation energy from said flame and said body onto said device, said device being operably associated with said first and second channels, a member located, on the one hand, between said first and second channels, and on the other hand, said device, said member being movable to place said first and second channels alternately and sequentially in communication with said device, with the radiation energy from the body, in each instance, being substantially equal and occuring at equally spaced intervals, means including said device for deriving a control voltage having two differing frequency components, one frequency being low and corresponding to radiation energy from said flame alone, and the other frequency being high and corresponding to radiation energy from said body alone, control means for controlling the flow of fuel to said flame, said control means being sensitive and responsive to the presence of said low frequency, and frequency discriminating means receiving said high and low frequencies and transmitting to said control means only said low frequency so that the flow of fuel to said flame is maintained in the presence of and discontinued in the absence of said low frequency component.

References Cited in the file of this patent UNITED STATES PATENTS 1,755,970 Singleton Apr. 22, 1930 1,811,895 Ranger June 30, 1931 1,970,103 Runaldue Aug. 14, 1934 1,996,233 Darrah Apr. 2, 1935 2,304,641 Jones Dec. 8, 1942 2,404,147 Strickland July 16, 1946 2,404,903 Cohen July 30, 1946 2,621,808 Blakeney Dec. 16, 1952 2,696,876 Hartung Dec. 14, 1954 

